Anions in aqueous precipitation - Determination of Anions in Natural and Treated Waters - page 444

Table 5.8 Analysis of sulphate in rainwater

Sample mg L −1 added Ion selective electrode Found (mg L −1 ) %

B 3.57 3.57 ± 0.02 100.0 ±0.6

C 5.02 4.93 ± 0.08 98.2 ± 1.6

D 10.00 10.12±0.13 101.2 ± 1.3

400 a

4.00 4.06 ± 0.04 101.5 ± 1.0

500 a

8.33 8.24 ± 0.08 99.0 ± 1.0

Turbidimetric Found % mg L −1

B 3.57 3.5 ± 0.35 98.0 ± 10.0

Gravimetric Found % mg L −1

D 10.00

10.03 b 100.3 b

a Samples #400 and #500 were dilutions made from sample 'D'
b Only one analysis was performed
Source: Reproduced with permission from Marcel Dekker Inc [43]

It is seen in Table 5.8 that sulphates determined by this method are in good agreement
with gravimetric and turbidimetric results. Rainwater often contains copper and cadmium
and these ions interfere with and deactivate the lead electrode membrane surface.
However, they were present in such low concentrations and reacted slowly enough that
the rainwater samples could be analysed directly with no sample pretreatment. Because
of this interference, however, the electrode has to be repolished after each run. This
repolishing process takes about 30s.
Rainwater often contains copper and cadmium and these ions interfere with and
deactivate the lead electrode membrane surface. However, they were present in such low
concentrations and reacted slowly enough that the rain water samples could be analysed
directly with no sample pretreatment. Because of this interference, however, the electrode
has to be repolished after each run. This repolishing process takes about 30s.

5.1.11.6 Mass spectrometry

Ligon and Dorn [29] determined sulphate and nitrate in rain water by mass spectrometry.

5.1.11.7 Ion chromatography

The application of this technique is discussed under multianion analysis in sections
5.1.14.3 and 12.4.1.